The present invention relates to an exposure device for an image forming apparatus and, in particular, to an exposure device used in a plurality of optical systems, such as a color copier and color printer.
In recent times, an image forming apparatus, such as a color copier and color printer, for forming a color image on a sheet with the use of a plurality of color toners has been increasingly used. This type of image forming apparatus is equipped with an exposure device for deflecting a plurality of laser beams for respective colors and, by doing so, scanning an image carrier with the exposure beams.
This exposure device has a plurality of laser beam sources for emitting laser beams on the basis of image data of respective colors. The respective laser beam sources are unitized with, for example, lenses and lens stops which shape the cross-sectional configuration of the laser beams to a desired configuration and provide light emitting units.
The laser beams for respective colors emitted through the stops from the respective light emitting units are combined respectively through a galvanomirror, half mirrors, cylindrical lens and are incident on the polygon mirror. The laser beams for respective colors reflected on the polygon mirror are illuminated through the fxcex8 lenses onto an exposure light position on the photosensitive drum. Through the rotation of the photosensitive drum and the rotation of the polygon mirror, the laser beams for respective colors scan the surface of the photosensitive drum as exposure beams to form electrostatic latent images for respective colors on the drum surface.
If, however, respective stops are provided on the corresponding light emitting units for respective colors, then xe2x80x9cshapedxe2x80x9d laser beams are incident through the above-mentioned optical members onto the polygon mirror and the incident positions of the laser beams for respective colors are liable to be shifted, thus presenting a problem.
If the incident positions of the respective laser beams are so shifted relative to the polygon mirror, the latent images of respective colors formed on the drum surface are displaced, thus creating a color shift on a resultant image.
Further, the laser beam which has been passed through the stop is conducted through a plurality of optical members to the polygon mirror and, therefore, there are sometimes the cases where it is not possible to adequately exhibit the desired performance of the respective optical members.
The present invention is achieved with the above in view and the object of the present invention is to provide an exposure device which can be made simpler in structure and further can shiftlessly direct a plurality of laser beams onto an image carrier as exposure beams without lowering their strengths.
In order to achieve the above-mentioned object of the present invention, an exposure device of the present invention comprises a plurality of light emitting sections which emit laser beams on the base of respective image signals; a deflecting/scanning section which deflect the plurality of laser beams emitted from the corresponding light emitting sections and scan an image carrier with the exposure beams to form latent images on the image carrier on the basis of respective image signals; a pre-deflection optical system which allow the laser beams emitted from the plurality of light emitting sections to be combined and the combined beams to be conducted to the deflecting/scanning section; and a single common optical member provided at a position downstream of the pre-deflection optical system along an optical path of the laser beams but upstream of the deflecting/scanning section, to allow the combined beams to be passed and a cross-sectional configuration of the combined beams to be shaped.
Further, an image forming apparatus of the present invention comprises an image carrier; an exposure device which form latent images on the image carrier on the basis of image signals; a developing device which supply toners to the latent images to effect development; a transfer unit which transfer a resultant toner image to a sheet; and a fixing device which fix the transferred toner image to the sheet, wherein the exposure device comprises; a plurality of light emitting sections which emit laser beams on the basis of the image signals; a deflection/scanning section which deflect laser beams emitted from the light emitting sections and scan the image carrier with the exposure beams; a pre-deflection optical system which allow the laser beams emitted from the plurality of light emitting sections to be combined and the combined beams to be conducted to the deflecting/scanning section; and a single common optical member provided at a position downstream of the pre-deflection optical system along an optical path of the laser beams but upstream of the deflecting/scanning section, to allow the combined laser beams to be passed and a cross-sectional configuration of the combined beams to be shaped.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.